Micro-Electro-Mechanical Systems (MEMS) are typically employed because of their almost ideal isolation, which is a critical requirement for wireless radio applications where they are used for mode switching of power amplifiers (PAs) and their low insertion loss (i.e., resistance) at frequencies of 10 GHz and higher. Depending on the particular application and engineering criteria, MEMS can come in many different forms. For example, MEMS switches can be realized in the form of a cantilever beam structure or a bridge beam structure.
In the cantilever structure, a cantilever arm (suspended electrode with one end fixed) is pulled toward a fixed electrode by application of an actuation voltage. The voltage required to pull the suspended electrode to the fixed electrode by electrostatic force is called pull-in voltage, which is dependent on several parameters including the length of the suspended electrode, spacing or gap (cavity) between the suspended and fixed electrodes, and spring constant of the suspended electrode, which is a function of the materials and their thickness.
MEMS can be manufactured in a number of ways using a number of different tools. In general, though, many of the methodologies, i.e., technologies, employed to manufacture MEMS have been adopted from integrated circuit (IC) technology. For example, almost all MEMS are built on wafers and are realized in thin films of materials patterned by photolithographic processes on the top of the wafer. In particular, the fabrication of MEMS uses three basic building blocks: (i) deposition of thin films of material on a substrate, (ii) applying a patterned mask on top of the films by photolithographic imaging, and (iii) etching the films selectively to the mask.
CMOS processes are known to have processing variability, which may affect the MEMS and, more particularly, cavity dimensions and placement of the beam electrode (i.e., suspended electrode). The variability of these dimensions and placement of the beam can affect the pull-in voltage. For example, in MEMS cantilever type switches, the suspended electrode is formed on a sacrificial material, which will form the cavity structure; however, due to processing variability, the cavity and hence placement of the suspended electrode may not be within design specifications for a particular pull-in voltage. This is typically due to the variability in thickness of the sacrificial cavity material deposited under the suspended electrode of the MEMS structure. More specifically, this variability may be due to silicon deposition/CMP/deposition processes. This variability can also be the result of an oxide deposition and CMP variability, which also adds to the sacrificial cavity material (e.g., silicon) thickness variability component.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.